The current trend in automotive passenger vehicle design is toward lower power-to-weight ratios and reduced axle ratios. The objective of such vehicle design is to achieve greater fuel economy and reduced emissions by reducing the number of engine revolutions per mile. To achieve this objective, vehicle performance may be reduced to such an extent that towing ability could become unacceptable.
The occasional need for greater towing ability can be met by an auxiliary underdrive transmission of moderate ratio. Such an underdrive transmission should be shiftable manually, either to direct drive or reduction ratio drive, with the vehicle stationary. The underdrive transmission should be capable of running continuously in either direct or ratio. It should be simple, inexpensive, and capable of being mounted at the output of a conventional automotive transmission.